Currently, for such well-known display devices as a liquid crystal display (LCD), an electroluminescence (EL) display panel and an electronic paper, thin film transistors (TFTs) for controlling pixel switches are arranged on a display substrate for achieving a display function. As the switches for the pixels, these TFTs are used to control the transmission of data signals from data lines into the pixels, so as to display an image. However, during the actual manufacture of the display substrates, usually there are differences in TFT characteristics between different display substrates and between different regions of an identical display substrate due to an unstable process capability. When a defective process step remains unknown, a technician may select a new set of glass substrates and rotate them prior to different process steps. After the display substrates have been completed, the TFT characteristics of these display substrates may be tested, and then compared with the TFT characteristics of the previous display substrates, so as to find the problems in devices for manufacturing the display substrates, thereby to improve the process as well as the product quality.
For an existing process for manufacturing a TFT array substrate, its TFT characteristics may be monitored and tested by forming a TFT at a peripheral region of the display substrate identical to that at a pixel region, and a gate electrode, a source electrode and a drain electrode of the TFT are connected to testing terminals G, S and D, respectively. In addition, usually a vacant testing terminal E is also provided. As shown in FIGS. 1a and 1b, when the TFT characteristics are tested, usually a voltage signal of −30V to 30V is applied to the testing terminal G, a constant signal of 15V is applied to the testing terminal S, a change in a current flowing through the TFT is collected by the testing terminal D, and no signal is applied to the testing terminal E. Probes of a testing device are located at fixed positions, i.e., at four vertices of a square, and spaced apart from each other at an interval of 700 μm. During the TFT characteristics testing, the signals are applied to the testing terminal G and the testing terminal S in FIG. 1a through the probes of the testing device before rotation of the display substrate, and a collected current signal is transmitted by the testing terminal D through the probes to the testing device, so as to collect testing data. Identically, after the display substrate is rotated by 180°, the signals are applied to the testing terminal G and the testing terminal S in FIG. 1b through the probes, the collected current signal is transmitted by the testing terminal D through the probes to the testing device, so as to collect the testing data. By comparing the testing data collected before and after the rotation of the display substrate, it is able to find the problems in devices for manufacturing the display substrate, thereby to improve the process as well as the product quality.
However, during the above testing, as shown in FIGS. 1a and 1b, the TFT and the testing terminals rotate along with the display substrate, but the positions of the four probes of the testing device are fixed. Hence, it is required to change the positions of the probes and the applied signals, thereby to test the TFT characteristics normally before and after the rotation. As a result, the testing is complicated and time-consuming.
Hence, there is an urgent need to simplify the testing of the display substrate and find the problems in the manufacturing process rapidly, thereby to improve the testing efficiency, the manufacturing process and the product quality.